1. Field of the Invention
The present invention relates to an etching reagent for manufacturing a wiring using low resistance copper, and a method for manufacturing an electronic device substrate and an electronic device.
2. Description of the Related Art
An example of electronic devices comprises a thin film transistor type liquid crystal display device.
FIG. 9 is an illustrative drawing of the conventional thin film transistor type liquid crystal display device.
A gate electrode 84 comprising a conductive material such as Al or an Al alloy is provided on a substrate 83 of this thin film transistor 82, and a gate insulation film 85 is provided so as to cover the gate electrode 84. A semiconductor active film 86 comprising an amorphous silicon (abbreviated as a-Si hereinafter) is provided on the gate insulation film 85 above the gate electrode 84, and a source electrode 88 and a drain electrode 89 comprising a conductive material such as Al or an Al alloy are provided via an ohmic contact layer 87 comprising an amorphous silicon containing a N-type impurity such as phosphorus (abbreviated as a N+-type a-Si hereinafter) from the semiconductor active film 86 through the gate insulation film 85. A passivation film 90 is provided so as to cover the thin film transistor 82 composed of these source electrode 88, drain electrode 89, gate electrode 84 and the like, and a contact hole 91 is provided through the passivation film 90 on the drain electrode 89. A pixel electrode 92 comprising a transparent electrode layer comprising indium tin oxide (abbreviated as ITO hereinafter) that is electrically connected to the drain electrode 89 trough the contact hole 91 is additionally provided.
The left portion of FIG. 9 shows a cross sectional structure of a gate terminal pad portion 93 at the end of the gate wiring located at outside of the display area. A contact hole 95 perforating through the gate insulation film 85 and passivation film 90 is provided on a lower pad layer 94 comprising a gate wiring material such as Al or an Al alloy on the substrate 83. An upper pad layer 96 comprising a transparent electrode layer, which is electrically connected to the lower pad layer 94 through the contact hole 95, is also provided.
The problem of retardation of signal transmission due to the resistance of electrodes such as the gate electrodes, source electrode, and drain electrode, and the resistance of wiring such as the gate wiring, source wiring and drain wiring have became apparent in compliance with the recent development of the high speed liquid crystal display device. Accordingly, use of copper having a lower resistance than that of Al or an Al alloy has been studied for solving the problems as described above. The materials constituting the electrode such as the gate electrode are also included in the wiring materials herein.
A Cu wiring can be formed, like constructing a wiring with Al or an Al alloy, by the steps comprising: forming a Cu film by a conventional sputtering method, forming a given mask pattern on the surface of the Cu film by photolithography, etching the Cu film using a given etching agent, and removing the Cu film except the area for forming the wiring.
The etching agents for Cu known in the art comprise PAN based (phosphoric acid-acetic acid-nitric acid based) etching agents, and ammonium peroxosulfate and acetic acid-hydrogen peroxide based etching agents, which have been frequently used for the etching agent for use in fine processing.
However, when a mask pattern 84b as shown in FIG. 10A, formed on the surface of a Cu film 84a deposited on a substrate 83a for forming a wiring, is subjected to etching by immersing it in an ammonium peroxosulfate based or PAN based etching agent in a stationary state, the Cu film 84a at the periphery of the mask pattern 84b is etched with an abnormally high etching rate to increase the amount of etching at the central portion at the side faces of the Cu film 84a more than the amount of etching at the remaining portions. As a result, the line width of the wiring 84c turns out to be narrower than the width of the mask pattern 84b (slimming phenomenon of the pattern) as shown in FIG. 10c. 
When a mixed solution of acetic acid and hydrogen peroxide or a ammonium peroxosulfate solution is used as an etching agent, it is difficult to control the immersion time of the Cu film since the etching rate is vigorously changed with time, thereby making it difficult to obtain a Cu wiring having a desired line width. However, the slimming phenomenon as described above is not observed when the acetic acid-hydrogen peroxide based etching agent is used.